The last-mile broadband data access may be implemented in many modes in a communication system, and an x Digital Subscriber Line (xDSL) is a common access mode. The merit of the xDSL lies in using twisted pairs to transmit data. Therefore, the xDSL shares lines with the Public Switched Telephone Network (PSTN) instead of distributing new cables. In the service processing, services are differentiated through signal bands. Specifically, the PSTN service employs analog signals and its frequency band is generally a range that locates below 4 kHz; and the data service employs the signals on the frequency band that locates above 4 kHz. Proper filtering prevents interference between the two services.
Currently, a common type of broadband communication equipment at the customer premises is known as a Customer Premises Equipment (CPE) or Home Gateway (HGW). In an uplink direction, the CPE or HGW may be connected with the Digital Subscriber Line Access Multiplexer (DSLAM) at the Central Office (CO) through xDSL twisted pairs. In a downlink direction, the CPE or HGW may be connected with the interfaces such as Fast Ethernet (FE) interface, Universal Serial Bus (USB) interface, Plain Old Telephone Service (POTS) interface, and WiFI interface. The data is compressed within the CPE product. The downlink POTS interface may be connected with a telephone set directly. Sampling, compression and packaging of an analog signal are performed within the product, so that the analog signal is converted into a data signal compatible with the xDSL protocol, and data is exchanged with the DSLAM at the CO. In such a process, a Voice over IP (VoIP) call can be dialed through a traditional analog telephone set.
Generally, the product has a Foreign Exchange Office (FXO) interface for shifting the call from the VoIP to the PSTN. That is, when the equipment at the xDSL central office fails, all data services are impossible, but the calls attached to the POTS interface can be dialed through the PSTN line.
In the existing home telephone service system, the home telephone service system from the CO of the operator to the user is connected through a twisted pair system. The twisted pair system may bear Digital Subscriber Line (DSL) broadband data services or PSTN services. The cables of a home telephone service system are generally distributed in walls, and interfaces are led out in different rooms. (Currently, HGW is a common CPE.)
The HGW is connected with the twisted pair system through a DSL interface and enables data exchange in the uplink direction. FE interface may be connected with the devices such as computer and Set Top Box (STB) and enables access to the Internet in the downlink direction. The POTS interface may be connected with a plain telephone set or a facsimile machine and enables the VoIP function in the downlink direction. The USB interface may be connected with a printer or USB storage device and enables the relevant functions in the downlink direction. In the case of power off and no access of network, the telephone set connected with a POTS interface may implement a service of shifting a call from the VoIP to the PSTN through an FXO interface. The filter between the HGW and the twisted pair enables filtering, and prevents interference between low-frequency voice service and the high-frequency data service.
If the user only activates the data service (such as xDSL) instead of the PSTN service when the home telephone service system employs the foregoing HGW, only a first telephone set connected with the downlink POTS interface of the HGW is able to implement the telephone function (the telephone function is limited to the VoIP service), and a second telephone set and a third telephone set in other rooms are not able to implement the telephone function. If the telephone sets in other rooms also need to implement the telephone function, the cable distribution of the home telephone service system has to be modified to connect the two telephone sets to the downlink POTS interface of the HGW.
In view of the foregoing defects, the conventional art provides a solution: A detection module is added in the HGW to detect whether a PSTN service exists in the home telephone service system. If the PSTN service exists, the relay in the HGW is open, and the telephone set connected with the POTS interface and the telephone set in another room can make PSTN calls. If the data service is activated but the PSTN service is not available, the detection module reports the detection result to the CO and then closes the relay, and all telephone sets can be connected to the telephone service module of the HGW through the relay. The signals are sampled, compressed, and packaged, and converted into data streams compatible with the xDSL protocol to implement the function of making VoIP calls.
The conventional art has at least the following problems: If the DSLAM fails and thus is unable to process activation request signals, the HGW is unable to receive confirmation signals, further not able to close the relay, and therefore the telephone set is unavailable.